Market adoption of wireless LAN (WLAN) technology has exploded, as users from a wide range of backgrounds and vertical industries have brought this technology into their homes, offices, and increasingly into the public air space. This inflection point has highlighted not only the limitations of earlier-generation systems, but also the changing role that WLAN technology now plays in people's work and lifestyles across the globe. Indeed, WLANs are rapidly changing from convenience networks to business-critical networks. Increasingly users are depending on WLANs to improve the timeliness and productivity of their communications and applications, and in doing so, require greater visibility, security, management, and performance from their network.
Spectrum regulation has required that transmitters operating in the so-called radar channels or Dynamic Frequency Selection (DFS) channels, perform a “channel availability check” (CAC) prior to commencing transmissions on that channel. A channel availability check typically involves monitoring a candidate channel for 60 seconds to determine if radar transmissions are present. As spectrum regulation has given radar transmissions priority on the radar channel band, once radar transmissions are detected, wireless access points and their associated wireless clients must cease transmitting signals on that channel so as to not interfere with radar operations.
DFS is a mechanism that allows unlicensed devices to share spectrum with existing radar systems. The regulatory requirements for DFS have been adopted in the United States, Europe, and Japan, and these requirements are being considered by many other regulatory domains, which are considering the 5 GHz hands for unlicensed use. DFS specifies the types of radar waveforms to be detected and timing requirements for unlicensed operation in the DFS channel. DFS also specifies two different classes of devices: master device and slave device. A master device is a device that has radar detection capabilities and can control other devices in the network (e.g., an access point). A slave device is a device that does not initiate communication on a channel without authorization from a master device (e.g., a wireless client). Once a master device completes a CAC without detecting radar, the master device may transmit a DFS enabling signal, which allows slave devices to communicate with the master device.